Optical coupler packages contain at least one optical emitter device which is optically coupled to an optical receiver device through an optically transmissive medium. This arrangement permits the passage of information from one electrical circuit that contains the optical emitter device to another electrical circuit that contains the optical receiver device. A high degree of electrical isolation is maintained between the two circuits. Because information is passed optically across an insulating gap, the transfer is one way. For example, the optical receiver device cannot modify the operation of a circuit containing the optical emitter device. This feature is important because, for example, the emitter may be driven by a low voltage circuit using a microprocessor or logic gates, while the output optical receiver device may be part of a high voltage DC or AC load circuit. The optical isolation also prevents damage to the input circuit caused by the relatively hostile output circuit.
A common optical coupler package format is the dual-in-line package or DIP. This package is widely used to house integrated circuits and is also used for conventional optical couplers. Various versions of optical coupler DIP packages having 4, 6, 8 or 16 pins are commonly manufactured.
An improved optical coupler package is shown in FIG. 1(a). FIG. 1(a) shows a perspective view of an optical coupler package 900. It includes a substrate 902 and a “glob top” 906 comprising a light transmissive material. The glob top 906 covers the above-described optical emitter device and optical receiver device to protect them from the external environment. Solder balls 904 are on the substrate 902 and surround the glob top 906. In use, the optical coupler package 900 is flipped over and mounted to a circuit board or the like.
Although the package 900 shown in FIG. 1(a) is effective, as shown by the intermediate package structure 901 in FIG. 1(a), one problem that can occur during manufacturing is that the glob top 906 can overflow towards the pads 905 upon which the solder balls 904 (in FIG. 1(b)) would be located. The glob top 906 is generally deposited in a liquid or semi-solid form onto the substrate 902 and is cured. The uncured glob top 906 can flow before it is cured and can overflow onto the pads 905. If this occurs, then it may not be possible to place the solder balls 904 on the pads 905 and rework of the intermediate package structure 901 may be needed.
It is possible to separately deposit a dam structure on the substrate 902 to confine the glob top 906 as it is being formed. However, this requires additional process steps and adds to the overall cost of the package that is eventually formed. Also, the dam would only prevent the overflow of the glob top 906 as it is being formed. It would not serve any other function.
Embodiments of the invention address these and other problems, individually and collectively.